The invention relates to a method of driving a meter, the method comprising acting a pointer mounted on a drive unit by mounting the pointer on the drive unit composed of a stepping motor, a rotary magnet type ampere meter of the cross coil type, inputting in a predetermined cycle an amount of measurement from an object being measured, and outputting to the drive unit a change in the amount of measurement as an indicated value in predetermined unit of output updating cycle.
Conventional analog type indicating meters employ a stepping motor, a rotary magnet type ampere meter of the cross coil type, and so on. For example, a drive device for meters, having a drive unit composed of a stepping motor comprises a drive circuit for driving the stepping motor on the basis of a digital signal conformed to an amount of measurement, and a pointer mounted on a drive shaft end of the stepping motor to indicate graduation on a dial plate, which corresponds to the amount of measurement, thereby representing the amount of measurement.
Such drive device for meters can be used in, for example, a running speedometer and an engine speedometer for automobiles, and further in a fuel meter and a thermometer with an A/D processing of a detected signal, and various proposals for such drive device having been presented for commercial application, such as disclosed in Japanese Patent Laid-Open Nos. 129575/1986, and 223312/1988. Recently, serial communication has prevailed in meters for vehicles, and drive devices have been developed, which drive respective meter bodies by transferring to respective meters through a serial transmission cable from an ECU (Engine Control Unit) loaded on a vehicle a digital signal conformed to a running condition of the vehicle. When respective meters are to be driven through such serial communication control, there is involved a problem that even gentle changes in amounts of measurement become rapid changes on sides of the indicating meters to provide no smooth indicating action on the indicating meters since an output updating cycle presents itself in unit of 50 msec when a cycle (input cycle) of amounts of measurement inputted into a processing unit (processing circuit) for acting the indicating meters is 50 msec even if an output updating cycle of a processing circuit itself for driving a drive unit composed of a stepping motor has a capability of 5 msec in a speedometer and a tachometer for indicating a speed of car and an engine revolution, of which amount of measurements change much.
In particular, with stepping motors, correction of drive signal waveform provides smoothness on the basis of a stepping motion, which corresponds to a pitch of teeth on a comb-shaped yoke.
Such stepping motors involve a problem that a change in a drive signal to a stepping motor becomes great when an updating cycle of measurement data is great relative to a change in an amount of measurement, and the stepping motor itself is excellent in responsiveness, whereby when a change in data in a period of output updating is great conversely, such great change is ascertained to immediately give rise to an intermittent motion on a pointer, thus not obtaining any smooth indicating action in indicating meters.
Hereupon, the invention takes notice of the above-mentioned problem, and provides a method of driving a meter, in which an intermittent motion on a pointer is prevented and a smooth indicating motion is obtained in an indicating meter.
The invention relates to a method of driving a meter by inputting into a processing unit in a predetermined cycle an amount of measurement from an object being measured, and outputting to a drive unit a change in the amount of measurement as an indicated value in predetermined unit of output updating cycle of the processing unit to act a pointer mounted on the drive unit.
The invention provides a method of driving a meter comprising using a predetermined function to obtain an indicating characteristic, which determines a behavior of the pointer, on the basis of an indicated value of the pointer in the past, an indicated value of the pointer determined at the present time, and a target value, which acts the pointer in response to the amount of measurement, to thereby act the pointer with the indicated value along the indicating characteristic in the unit of output updating cycle.
A first driving method comprises sequentially inputting into the processing unit first and second target values to act the pointer in accordance with the amount of measurement, comparing the first target value and the second target value with each other when acting the pointer toward the first target value from an indicated value of the pointer determined at the present time, judging whether the second target value tends to be increased or decreased relative to the first target value, using a predetermined function to obtain an indicating characteristics, which indicates a value equal to or more than the first target value from the indicated value of the pointer determined at the present time, in the case where the second target value tends to be increased, and an indicating characteristics, which indicates a value equal to or less than the first target value from the indicated value of the pointer determined at the present time, in the case where the second target value tends to be decreased, and acting the pointer by means of an indicated value in the unit of output updating cycle in accordance with the indicating characteristics,-so that the pointer can be smoothly acted as compared with the case where the pointer is acted by the indicated value in unit of output updating cycle in accordance with the indicating characteristics, which is obtained by simply linearly connecting indicated values obtained in at a predetermined input cycle.
Also, a second driving method comprises inputting a target value to act the pointer in accordance with the amount of measurement, using a predetermined function to obtain an indicating characteristics, which indicates a first indicated value when acting the pointer toward the target value from the first indicated value of the pointer determined at the present time, and which approximates a second indicated value, which becomes a target value of the pointer in the past, and the target value, and acting the pointer by means of an indicated value in the unit of output updating cycle in accordance with the indicating characteristics, so that the pointer can be smoothly acted as compared with the case where the pointer is acted by the indicated value in unit of output updating cycle in accordance with the indicating characteristics, which is obtained by simply linearly connecting indicated values obtained at a predetermined input cycle.